This invention relates to sheet handling apparatus for picking sheets from one or more stacks of sheets and presenting the picked sheets to an outlet point.
The invention has application in cash dispenser units provided as part of automatic teller machines (ATMs). Such units dispense currency notes and include one or more cassette holders for cassettes each containing a stack of currency notes of a particular denomination, usually with different cassettes containing notes of different denominations. Pick mechanisms are associated with each cassette holder to pick notes from the stacks in the cassettes. The notes are then carried by suitable transport means to an outlet point for removal by the customer.
The pick mechanisms may include suction pads for picking the notes one by one from the cassettes and the suction pads are made operational by connection to a vacuum pump. An example of a pick mechanism is described in European Patent Application No. 486251A. A suitably powerful electric motor is required to operate the pump as well as to provide motive power to sheet transport means to carry the notes away from the pick mechanisms. It is also desirable to be able to accurately position the notes when they approach the outlet point. This requirement would be satisfied by using a stepper motor to drive the transport means. However using a stepper motor as the sole source of motive power for the entire apparatus would require a large and hence expensive motor and associated pulse generator. If instead a conventional (and cheaper) ac induction motor is used to operate the vacuum pump and drive the initial part of the sheet transport and the function of the stepper motor is limited to drive the final part of the transport, then problems will occur at the point at which the notes cross over from one drive to the other. If the initial transport is running more slowly than the final transport then the notes are at risk of being ripped, particularly if they already have a small tear. Conversely if the initial transport is running faster than the final transport then the notes are liable to crumple and cause a jam. With a conventional ac induction motor the speed tolerance may be as much as .+-.20% depending on load.